Potassium Hydrogen Tartrate

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Potassium Hydrogen Tartrate

Potassium hydrogen tartrate is an acid salt of tartaric acid. It is denoted by the chemical formula KC₄H₅O₆ and has a molecular weight of 188.18. It is made up of 25.53% carbon, 51.01% oxygen, 20.78% potassium, and 2.68% hydrogen, and has a density of 1.95 g/cc. When purified, it is an odorless, white, crystalline powder that has a pleasant acidulous taste. It is used as a leavening agent in baking powders and forms naturally during wine fermentation.

Properties

Potassium hydrogen tartrate is known by a variety of names including potassium bitartrate, potassium acid tartrate, cream of tartar, and faeccula. An impure form of potassium hydrogen tartrate, called argol, is formed naturally during the fermentation of a variety of fruit juices. It is found as a crystal residue in wine casks.

One gram of potassium hydrogen tartrate dissolves in 162 ml water. When the water temperature is increased, so is its solubility. Using boiling water, one gram will dissolve in about 16 ml of water. The material is insoluble in absolute alcohol. The saturated aqueous solution has a pH of approximately 3.5. In this solution the material dissociates into its component ions, one of which is tartaric acid. This acid was first isolated and characterized in 1769 by chemist Carl Wilhelm Scheele. He obtained it by boiling cream of tartar with chalk and then treating it with sulfuric acid.

Production

Potassium hydrogen tartrate has been known for centuries. The ancient Greeks and Romans, who found it as a deposit from fermented grape juice, called it tartar. Today, cream of tartar is manufactured from the waste products of the wine industry. Waste products include press cakes from unfermented or partially fermented grape juice, dried slimy sediments from wine vats, and crystalline crusts from the wine vats used in second fermentations. The crystalline material is scraped off the sides of the vats and then purified to at least 99.5%.

Uses

Cream of tartar is used for a wide variety of applications. It is one of the primary components in baking powder. Here it functions as a leavening agent. Leavening agents are compounds that are put into products like breads and rolls to generate carbon dioxide. The carbon dioxide is trapped in the batter creating air pockets that result in products that are lighter and crispier. In baking powder, cream of tartar specifically functions as the acidic portion that reacts with the basic component, sodium bicarbonate, to generate carbon dioxide gas. The limited solubility of cream of tartar in cold water helps prevent premature leavening. This is useful when mixing dough.

Beyond leavening, cream of tartar also functions as an acidulant in food products. Acidulants serve a variety of purposes in this capacity, but their major role is to make foods more palatable. Acidulants can also be used as flavoring agents because they can intensify certain tastes and mask undesirable aftertastes. They can act as buffers to control the pH during processing. They also have an antimicrobial effect and can prevent the production of spores. They are synergistic with antioxidants which means they help make antioxidants more effective. Acidulants are also viscosity modifiers. By using the appropriate concentration a batter can be made thicker or thinner. They are also melting modifiers and meat curing agents. The addition of cream of tartar to candy and frosting recipes results in a creamier consistency. It can also help improve the stability and volume of egg whites if added before beating.

KEY TERMS

Acid— A substance that produces hydrogen ions when placed in an aqueous solution.

Acidulant— A food additive that improves flavor, controls pH, acts as a preservative, and modifies the viscosity of baked goods recipes.

Antimicrobial— A material that inhibits the growth of microorganisms that cause food to spoil.

Fermentation— A process by which complex organic molecules are enzymatically broken down to simpler molecules. For example, in alcohol fermentation glucose is reduced to ethyl alcohol and carbon dioxide.

Leavening agent— A compound used in baking to produce carbon dioxide in a batter. It creates air pockets in gluten-based food products.

Solubility— The amount of a material that will dissolve in another material at a given temperature.

Non-food applications of potassium hydrogen tartrate include its use as one of the starting materials for the production of tartaric acid. It also finds use in metal processing for such things as coloring and galvanic tinning of metals. In the production of wool it is used as a reducer of CrO₃ in mordants. In the pharmaceutical industry it has been used for its cathartic effect. Veterinarians use it as a laxative and diuretic. Cream of tartar is classified as a generally regarded as safe (GRAS) compound for use in food and beverage products.